Begin by combining the sugar, maple syrup, and 1/2 cup of water in the pot. Stir well to combing the ingredients making sure the water and syrup saturate the sugar. Heat the mixture stirring slowly over medium heat until it comes to a slow boil.
Next, cover the pot with the lid and let it cook for 2-3 minutes over medium heat. After 3 minutes have passed, remove the lid and let the condensation run down the sides of the pot. ( You do not want any unmelted sugar on the sides of the pot).
After covering for an additional minute, remove the lid and insert a candy thermometer. Continue cooking on medium heat until syrup reaches 242°F.
In the mean time, combine 1/2 cup water and the gelatin in your stand mixer bowl. Allow the gelatin to fully absorb the water for around 10 minutes.
Once the syrup has reached a temperature of 242° on the candy thermometer, remove it from the heat. Allow the syrup to rest for a moment, and the bubbling to stop.
Meanwhile turn the stand mixer on at medium speed. Slowly pour the syrup into the mixing bowl allowing it to flow down the sides. This cools the syrup enough to prevent scorching of the gelatin.
After the syrup has incorporated with the gelatin, add in your salt. Next, allow the mixer to remain at medium speed for 3 minutes. The mixture should double in size. Once the syrup has doubled, turn the mixer to high speed and continue whisking for another 3 minutes. Add in the vanilla flavoring and continue mixing for 1 additional minute.
Butter your spatula to prevent sticking, and transfer the marshmallow mixture to an 8X8 pan lined with parchment paper. Finally, allow the mixture to set for at least 8 hours. I let it set overnight.
After the marshmallow have completely set, cut the into squares. Lastly, combine the powdered sugar and cornstarch. Dust the edges of the marshmallows in the cornstarch to prevent sticking.